Intelligence quotient (IQ) is the total score of standardized tests that assess intelligence. It is not an absolute "measure of mind" but an estimate of where a person stands relative to others of the same age.
How the scale is built
Modern tests use the deviation IQ: raw scores are converted to a normal distribution with a mean of 100 and a standard deviation of 15. About two thirds of people score 85–115, roughly 2% score above 130 and 2% below 70.
The historical formula and mental age
Originally William Stern and Lewis Terman calculated IQ as a ratio: (mental age ÷ chronological age) × 100. A child performing exactly at their age got 100. The "ratio" formula was abandoned in favor of the deviation approach — for more, see mental age.
The Flynn effect
Over the 20th century raw scores rose by about 3 points per decade — this is the Flynn effect, which is linked to the environment (nutrition, education). In several countries a reverse trend — falling scores — has been noted for generations born after ~1975.
IQ, health and aging
Cognitive epidemiology shows that intelligence measured early in life is a significant predictor of later health and mortality. But IQ is only one facet: with age the dynamics matter more, reflected by cognitive reserve and cognitive aging.
Calculate using this marker
Calculators where IQ (Intelligence Quotient) is used directly:
Frequently asked questions
Is a high IQ a guarantee of success and health?
No. IQ is statistically linked to education, income and health, but it is only one factor. Personality traits (for example, conscientiousness), skills and environment often matter just as much, and sometimes more.
Is IQ fixed for life?
Relative standing is fairly stable but not absolute: scores are influenced by education, health and motivation. Individual cognitive functions change differently with age — some decline, while vocabulary often grows.